1. Field of the Invention
This invention relates to a shutter for a camera of the type in which a shutter base plate is made of a synthetic resin.
2. Description of the Related Art
FIG. 3 of the drawing shows a conventional focal-plane shutter for use in a camera.
In this focal-plane shutter, on a shutter base plate 1 are mounted blade driving lever shafts 2 and 2' with main arm rotating shafts 2a and 2a' respectively, formed at one end thereof, a charge lever shaft 3 which serves as the rotational center of a charge lever (not shown) for charging the blade driving lever shafts 2 and 2', auxiliary arm rotating shafts 4 and 4', and shafts 5 and 6a, 6b and 6c through which a cover plate 13 is mounted on the shutter base plate 1. The shutter base plate 1 has an aperture 7 formed therein. The above-described shafts 2, 2', 3, 4, 4', 5, 6a, 6b and 6c are respectively fitted in holes 8a to 8i formed in the shutter base plate 1 by means of caulking. Holes 9 and 9', along which the charge lever (not shown) is pivoted, are also formed in the shutter base plate 1. A group of leading blades 10 includes a slit forming blade 10c and separate blades 10 d. The blades 10c and 10d are linked to a main arm 10a and an auxiliary arm 10b through caulked portions 10e and 10e'. The main arm 10a is pivotally supported on the main arm rotating shaft 2a of the blade driving lever shaft 2, and the auxiliary arm 10b is pivotally supported on the auxiliary arm rotating shaft 4. A group of trailing blades 11 includes a slit forming blade 11c and separate blades 11d. The blades 11c and 11d are linked to a main arm 11a and an auxiliary arm 11b through caulked portions 11e and 11e'. The main arm 11a is pivotally supported on the main arm rotating shaft 2a', whereas the auxiliary arm 11b is pivotally supported on the auxiliary arm rotating shaft 4'. A partitioning plate 12 is disposed between the group of leading blades 10 and the group of trailing blades 11 so as to prevent any interference between the two groups. The partitioning plate 12 has an opening 12a corresponding to the aperture 7. A cover plate 13 is made of a thin metal plate, as is the shutter base plate 1. The cover plate 13 has an opening 13a corresponding to the aperture 7. In order to ensure smooth movement of the blades 10 and 11, the leading ends of the blades 10c, 10d, 11c and 11d are arranged to slide along spacers 14 and 15.
In the above-described conventional shutter structure, since the blade driving lever shafts 2 and 2', the charge lever shaft 3, the auxiliary arm rotating shafts 4 and 4', and the shafts 5, 6a, 6b and 6c must be caulked in the holes 8a to 8i formed in the shutter base plate 1, the manufacture of a shutter base plate unit is a time-consuming task, which increases the cost of production.
Accordingly, it has been proposed to reduce production costs and simplify the shutter manufacturing processes by preparing a shutter base plate with the above-described various shafts formed integrally therewith by the molding of a synthetic resin. However, the shutter base plate is a thin member. A shutter base plate formed by the molding of a synthetic resin may be deformed by the application of force to the blade driving levers or the charge lever. Such deformation of the shutter base plate will adversely affect the operation of the blades, deteriorating the precision of a shutter exposure (shutter time), and in the worst case, causing breakage of the shutter base plate due to its insufficient strength.
Molding of a synthetic resin into a shutter base plate with integrally formed shafts is proposed in the specification of Japanese Laid-Open Utility Model Application NO. Sho 58-16625.
However, the shutter base plate proposed in the above-described application has a configuration in which a plurality of thin pressed metal plates are laminated on top of each other or in which a thin metal plate is inserted in the synthetic resin that forms a shutter base plate during the molding so as to increase its strength, and it is not prepared by merely molding a synthetic resin. A shutter base plate formed solely by molding a synthetic resin is disclosed in the specification of U.S. patent application Ser. No. 217,649 filed on Jul. 12, 1988.
In the shutter structure shown in FIG. 3, the edge portion of the aperture 7 of the shutter base plate 1 must be bevelled to form a bevelled portion 7a. This secondary machining is required to make the blades operate smoothly. Furthermore, the shutter base plate 1 is made of a metallic material, and the end surface thereof is made flat. These aspects increase the intensity of harmful light reflected by the end surface, increasing the possibility that a photographic film will be adversely affected by reflected light.
This adverse affect on the film in the conventional shutter shown in FIG. 3 will be described below in detail with reference to FIG. 6. Since the shutter base plate 1 is mounted on a lensboard unit of a camera body, harmful light 71 that has passed through a lens and that is incident on the shutter from the side of the shutter base plate 1 is reflected by a flat end surface 7b of the aperture 7. The reflected light 72 reaches a film 50 located on the side of the cover plate 13.
Consequently, a reflection preventing coating is required on a conventional camera shutter. Further, it is impossible to block harmful reflected light completely by the coating conventionally applied in a conventional camera shutter.